Conduits for fluids, such as water or sewage conduits, or gas or chemical pipe, deteriorate over time. For example, many of the water mains throughout North America are made from unlined cast-iron pipe, the preferred material for water distribution systems up to the mid-1970's and beyond. Over time such pipes will deteriorate, often due to corrosion, becoming pitted and forming tubercules. This corroded material, in combination with mineral deposits, is known as encrustation and tuberculation.
Such deterioration results in leakage of the fluids, such as water or sewage, into the surrounding environment. For example, in 2013, Toronto experienced approximately 1700 water main breaks. These cause drops water pressure drops, and the leaking fluids can weaken the surrounding ground and can interfere with other underground systems, such as communication systems or other water or fluid bearing conduits. Such conduits need to be rehabilitated.
One approach to rehabilitation is to replace the deteriorated conduit. However, this can be a very costly and labour-intensive exercise; for example, if the conduit is a buried water pipe, replacement involves setting up a work area and digging up the pipe, known as “open-cut replacement”.
A different approach to rehabilitation is to re-line the walls of the conduit, which can be performed without digging up or accessing the exterior of the conduit itself. In the water conduit rehabilitation sector, this is known as “trenchless technology”. In doing so, a “structural liner” is formed; put simply, a new pipe or conduit (or inner surface) is formed inside the old conduit. As a first step, it is usual for the conduit to be cleaned to remove debris, which can includes encrustation and tuberculation in the case of water conduits, but more generally can also include dust, grease and sludge.
The inside of the conduit is then lined. Two approaches are cured-in-place pipe and a cement-mortar lining.
Cement-mortar lining, also known as a spray-on liner, involves a cement mortar that is sprayed onto the inside of the conduit, sealing any leakages and so extending the useful life of the conduit. The spray is applied when the conduit is not in service, and is relatively dry.
Another solution is to deploy a cured-in-place structural liner within the conduit. For example, Canadian patent no. 2,361,960 of Mercier describes the use of a cured-in-place structural liner. The liner consists of two concentric tubular jackets (an outer and an inner jacket) made of a flexible material that are impregnated with an adhesive resin. Bonded to the inner surface of the inner jacket is a film that is impermeable to liquid to flow through the conduit. The liner is inserted into one end of a dry conduit and then pulled into place. A shaping step then occurs, where the liner is made to conform to the inner wall of the conduit. The liner is then cured in place by flowing heated water through the conduit. This causes the liner to become a rigid structure, bonded to the inner surface of the conduit.
In one example, such an approach results in a conduit lined with a polyurethane and fabric liner, typically 1/16 to ¼ of an inch thick, which is sealed in place with epoxy.
However, if the structural liner (whether a cured-in-place structural liner or a cement-mortar liner or another structural liner) is defective or improperly installed, it may need to be removed soon after installation. If the liner is misapplied or poorly applied (for example due to equipment failure, poor epoxy quality due to mix ratio and temperature), it may deform over time and may need to be removed in the medium term. Furthermore, in the long run structural liners themselves will deteriorate and need to be replaced. This will involve removing the installed liner.
There do exist devices or systems designed to clean conduits prior to liner installation. For example, U.S. Pat. No. 3,525,111 of Von Arx shows a device for treating the inner surface of a cylindrical duct, including rotating sets of arms. The arms may be equipped with bristles, scrapers, abrasives or paint applicators. The arms are rotated through use of a turbine when the device is towed through a fluid, or can be rotated by an electric or air motor. This device has at least two sets of rotating arms that rotate in opposite directions to reduce the impact of internal discontinuities in the pipe (such as rivet heads) on the desired treatment. U.S. Pat. No. 8,407,844 of Boe discloses a “pig” or device that moves through a pipe, powered by the flow of fluid in the pipe via a turbine, which may be used for cleaning. The tools in this device (for example, brushes or scrapers) may be powered by the turbine or by a power source such as a battery. U.S. Pat. No. 6,368,418 of Rowe discloses a device driven by water pressure in the conduit to move the device and rotate a disk with a serrated edge. U.S. Pat. No. 4,573,231 of Stockstein et al. also discloses a device driven by the water pressure in a conduit and driving a set of cutting wheels using a collar and impact shaft system. In another approach, U.S. Pat. No. 8,011,052 of Kapustin discloses a cleaning device that is designed to be towed by a pig towing device.
These approaches are designed to remove encrustation, tuberculation, or debris in the conduit. However, the removal of structural liners, including cured-in-place pipe and cement-mortar linings, presents a different problem than the scraping of deposits in the preparation for a lining.
Compared to encrustation, tuberculation, or debris, structural liners are generally harder, smoother, more strongly attached to the walls of the conduit, and broadly attached to the inner surface of the conduit. Although there may be deposits encountered in a conduit during cleaning that are hard, or smooth, or bonded to the inner walls of the conduit, such deposits are limited. In contrast, liners extend for the entire length and circumference of the conduit.
Generally, the prior art approaches to conduit cleaning provide cleaners with limited cutting and grinding power, often driven by turbines, or electric or air motors. For example, U.S. Pat. No. 6,368,418 of Rowe states that the device may need to be passed through a pipe several times for adequate cleaning of the pipe when removing deposits. Generally, these are either pushed through the conduit by differences in fluid pressure or are towed. Also, in practice rehabilitation of conduits using structural liners are performed using a dry pipe, while the devices listed above are often designed to work in a fluid environment.
In light of this, it would be advantageous to have a device for removing structural liners (whether cured-in-place liners or cement-mortar liners) from a dry conduit.